1. Field of the Invention (Technical Field):
The present invention relates to an interpenetrating polymer network (IPN) composition, especially a hydrophilic hydrogel composition for contact lens. More particularly, the present invention relates to polymerization of monomers in the presence of water soluble polymers as the IPN agents miscible with the monomer mixture using conventional crosslinkers or polymeric crosslinkers under ultraviolet and/or thermal curing condition.
2. Background Art:
Interpenetrating polymer network (IPN) technology has been undergoing development over the past several decades. An IPN consists of at least two types of polymers wherein one polymer is synthesized in the presence of an already existing polymer, or both polymers are synthesized simultaneously.
From a chemical point of view, an IPN is a whole unit structure formed from at least two distinct polymers. An IPN thereby has the physical and chemical properties of the constituent polymers, and thus combines the advantages of the polymers.
Hydrophilic hydrogels prepared by an IPN process have gained a great deal of attention in a variety of fields. The following patents disclose IPN hydrogels. U.S. Pat. No. 4,575,539 entitled “Drug delivery systems including novel interpenetrating polymer networks and method,” to DeCrosta, et al., issued Mar. 11, 1986, discloses an IPN employing hydrogel beads which is formed by swelling hydrogel beads with an acrylic type swelling agent and reacting the swelling agent with a crosslinking agent such as ethyleneglycol dimethacrylate. The system so produced has superior drug leading capacity and controlled release characteristics. U.S. Pat. No. 5,644,049, entitled “Biomaterial comprising hyaluronic acid and derivatives thereof in interpenetrating polymer networks (IPN),” to Giusti, et al., issued Jul. 1, 1997, discloses the use of hyaluronic acid and its derivatives in IPN to form a hydrogel. The IPN biomaterial so prepared is useful in many applications including dermatology, microsurgery, urology, and cardiovascular systems.
In the contact lens field, hydrogels are often formed by copolymerization of monomers with the appropriate crosslinkers. The following patents disclose hydrogels formed by copolymerization. U.S. Pat. No. 5,665,840, entitled “Polymeric Networks from Water-Soluble Prepolymers,” to Pöhlmann et al., issued Sep. 9, 1997, discloses a water-soluble, crosslinkable prepolymer having monomeric structural units of a vinyl lactam, vinyl alcohol, alkanecarboxylic acid vinyl ester, vinylic crosslinking agent, and a vinylic photo initiator. The patent further discloses water-soluble crosslinkable prepolymer having a copolymer chain comprising 5 to 85% by weight of a vinyl lactam, for example, N-vinyl pyrrolidone. A variety of N-vinyl lactams are disclosed according to a structural formula presented within. The most preferred vinyl lactam is N-vinyl-2-pyrrolidone. U.S. Pat. No. 4,430,458, entitled “Hydrogel-Forming Polymeric Materials,” to Tighe, et al., issued Feb. 7, 1984, discloses polymeric materials suitable for making contact lenses formed by copolymerization and crosslinking of an amide of an unsaturated carboxylic acid, an N-vinyl lactam, an ester of an unsaturated carboxylic acid, an unsaturated carboxylic acid, and a polymerizable hydrophobic vinyl monomer. This patent claims a contact lens in the form of a hydrogel comprising a crosslinked polymeric material containing units derived either by simultaneous copolymerization and crosslinking or by co-polymerization and subsequent crosslinking of the following monomers: 20 to 40 mole percent of an amide of acrylic of methacrylic acid; 25 to 55 mole percent of an N-vinyl lactam of the N-vinyl pyrrolidone type; 5 to 20 mole percent of an hydroxy alkyl ester of acrylic or methacrylic acid; 1 to 10 mole percent of acrylic or methacrylic acid; and at least about 5 up to about 10 mole percent of a polymerizable hydrophobic vinyl monomer. U.S. Pat. No. 4,022,754, entitled “Novel copolymer having utility as contact lens,” to Howes, et al., issued May 10, 1997, discloses a method to prepare terpolymers containing 3-methoxy-2-hydroxy-propyl methacrylate, N-vinylpyrrolidone, and methyl methacrylate, suitable for contact lens.
The use of an IPN hydrogel contact lens material has been found much less common, for instance, consider the following patents. U.S. Pat. No. 4,536,554, entitled “Hydrophilic polymers and contact lenses made therefrom,” to Lim, et al., issued Aug. 20, 1985, discloses the preparation of soft contact lenses made from IPN obtained by the polymerization of a mixture containing a hydrophilic vinylpyrrolidone monomer and a hydrophobic acrylic ester monomer in the presence of multiple crosslinking agents. U.S. Pat. No. 5,674,942, entitled “Interpenetrating polymer networks for contact lens production,” to Hill, et al., issued Oct. 7, 1997, discloses another IPN method using polyurea interlocked with polyacrylate; the former polymer is prepared from amines and isocyanates while the latter polymer is prepared from acrylic esters using a free radical initiator.
The following patents also disclose hydrogels:
U.S. Pat. No. 4,990,582, entitled “Fluorine-Containing Soft Contact Lens Hydrogels,” to Salamone, issued Feb. 5, 1991, discloses a soft contact lens material that exists as a hydrogel and is formed by a polymer containing a fluorinated monomer, a hydroxy alkyl ester of acrylic or methacrylic acid, and an N-vinyl lactam. According to the disclosure, an N-vinyl lactam is present from 5 to 80% by weight. The addition of the N-vinyl lactam is critical in combination with the fluoromonomer and the hydroxy alkyl ester of acrylic or methacrylic acid, to obtain clear bulk copolymers without any haze or opacity. The preferred N-vinyl lactam is N-vinyl pyrrolidone in concentrations from 5 to 80% by weight and preferably from 40 to 60% by weight. In the claims, about 10 to about 50 parts by weight of N-vinyl lactam is present.
U.S. Pat. No. 4,829,126, entitled “High Water-Absorptive Soft Contact Lens,” to Nakajima et al., issued May 9, 1989, discloses a highly water-absorptive soft contact lens made of a copolymer comprising 10 to 40 parts by weight of an acrylate or methacrylate polymer and 60 to 90 parts by weight of a hydrophilic monomer. To achieve a balance between structural integrity and water absorption, methacrylate monomers having a hydrophilic group are used, such as the N-vinyl lactam, N-vinyl pyrrolidone.
U.S. Pat. No. 4,620,954, entitled “Hydrogel from Ultraviolet-Initiated Copolymerization,” to Singer, et al., issued Nov. 4, 1986, discloses a contact lens hydrogel prepared by copolymerizing 70 parts of N-vinyl pyrrolidone and 23 parts of phenyl ethyl methacrylate, together with allyl methacrylate as a crosslinker, T-butyl peroctoate as a thermal initiator and 2,2-dimethoxy-2-phenylacetophenone or benzoin methyl ether as a photo initiator. The patent discloses N-vinyl pyrrolidone as a preferred N-vinyl lactam monomer and phenylethyl methacrylate as a preferred hydrophobic acrylate.
U.S. Pat. No. 4,440,919, entitled “Low N-Vinyl Lactam Content Based Biomedical Devices,” to Chromecek et al., issued Apr. 3, 1984, discloses N-vinyl lactam content copolymers that are crosslinked with resonance-free dye (alkine tertiary amine) cyclic compounds to obtain biomedical devices such as soft contact lenses. This patent also discloses the use of water-soluble diluents for use in the aforementioned polymer system to modify the physical properties of these properties. Such diluents are present, preferably, at not more than 30 weight percent. Diluents include low molecular weight, e.g., 500 to 10,000, linear poly (vinyl pyrrolidone).
U.S. Pat. No. 4,184,992, entitled “Cross-Linked Alkyl Methacrylate-N-Vinyl Lactam Polymer Composition for Use in Soft Contact Lenses,” to Hosaka, issued Jan. 22, 1980, discloses a crosslinked polymer composition prepared by polymerizing, using a bulk polymerization procedure, a monomer mixture comprising an alkyl methacrylate and an N-vinyl lactam in the presence of a crosslinking agent such as vinyl acrylate, vinyl methacrylate, triallyl isocyanurate and vinyl carboxylates. This patent discloses 2-hydroxyethyl methacrylate (“HEMA”)/N-vinyl pyrrolidone copolymer gels. Such gels are prepared by copolymerizing HEMA with N-vinyl pyrrolidone or graft-copolymerizing HEMA onto poly-N-vinyl pyrrolidone. A main point of this particular patent resides in the crosslinking agent used in combination with the methacrylate/N-vinyl lactam copolymerized mixture.
U.S. Pat. No. 4,045,547, entitled “Fabrication of Soft Contact Lens and Composition Therefor,” to Le Bouef et al., issued Aug. 30, 1977, discloses a contact lens composition comprising from 67.2% to 79.3% HEMA; from 14.25% to 35% PVP; from 0.1% to 4.04% EDMA; from 0.1% to 2.5% MA; from 0.1% to 5.0% water; from 0% to 4% PPMHQ inhibitor; and from 50 to 250 PPM MEHQ inhibitor.